1. Field of the Invention
The present invention relates to a gas engine electric power generating system. The system effectively utilizes coal mine methane gas which is low in methane concentration and large in its variation by the gas engine electric power generating system. Using coal mine methane gas also facilitates advancing economic development in developing countries by enabling these countries to profit from coal mine methane gas based electric power generation and also GHG (greenhouse gas) emission dealing.
2. Description of the Related Art
In growing awareness of a worldwide environmental problem, country-by-country objectives regarding reduction of carbon dioxide emissions were decided at the 3rd Conference of the Parties to the United Nations Framework Convention on Climate Change held in 1997 in Kyoto. In the meeting, a Kyoto mechanism was established for the reduction of GHG (CO2, CH4, N2O, etc.) emissions in accordance with the conditions of countries and for the promotion of the efficiency of reduction.
The Kyoto mechanism is a system to promote worldwide cooperation and emission credit dealing for the reduction of GHG. A concept of carbon dioxide emission credit (right to emit a certain amount of carbon dioxide) was introduced and which aims to utilize market principles as a supplementary scheme for achieving the reduction objective of each country. When each entity (nations, enterprises, stores, families, etc.) takes action of directly exhausting GHG (for example, consuming energy for operating machines, consuming gasoline for running vehicles, etc.) or when it takes action of indirectly exhausting GHG (for example, mining of coal, selling of gasoline, etc.), it is assumed that each entity is under an obligation to bear carbon dioxide emission credit corresponding to the exhausted amount of GHG.
As for energy, coal industries of major coal yielding nations of the world (China, CIS, Europe, and the United States, etc.) are expected to play an important roll as energy suppliers even in the middle part of this century.
However, in proportion to the coal production, methane gas of 10˜40 Nm3 (in terms of pure methane) per ton of coal is released to the atmosphere as recovered methane gas (30˜50% concentration, air diluted) and ventilated methane gas (0.3˜0.7% concentration, air diluted). Therefore, technology and business to effectively utilize the methane gas now being released to the atmosphere are very prospective and will make large social and economic contributions.
For example, the amount of coal mine methane gas released by countries & districts is; China 14,400(206), CIS 4,200(60), and other developing countries 3500(50) totaling to 22,100(316), which is over twice the total 11,000(157) of developed countries. (Units are in million m3/year, numbers in parentheses are the values converted to carbon dioxide in million tons/year). Utilizing the mine methane gas of developing countries is very advantageous for emission credit trading.
There are two kinds of coal mine methane gas as shown in FIG. 5. One is recovered methane gas recovered by a vacuum pump from bore holes for degassing for safety, and the other is ventilated methane gas exhausted together with the ventilation air from mine shafts and coal seams. The concentration of methane in these gases is low. For example, that of the former is 30˜50% and that of the latter is extremely low at 0.3˜0.7%.
To use a boiler or gas turbine as a heat engine to utilize methane gas has been considered.
However, if recovered methane gas having a methane concentration of 30˜50% is to be used for a gas turbine or boiler, as combustion temperature is low and methane concentration varies from time to time, it is not practical. It is difficult to use even the recovered methane gas for a gas turbine. Actually, the usage of recovered methane gas has been limited to use as a fuel by nearby households, or in the case of a boiler used only as auxiliary fuel.
Therefore, regarding the utilization of coal mine methane gas, even recovered methane gas is seldom utilized, and almost all of the coal mine methane gas is released to the atmosphere.
However, the greenhouse effect index (here and hereafter, this term is identical to “global warning potential”) of methane gas is 21 times that for methane gas that is burnt and released to the atmosphere as CO2. For example, coal mine methane gas release in China is 14.4 billion m3, which is equivalent to more than 10% of total amount of CO2 release in Japan.
Therefore, if Japan establishes an enterprise to effectively consume the coal mine methane gas in China to change the methane gas to CO2 and release to the atmosphere as CO2, a reduction of greenhouse effect index can be achieved. More specifically, a green house effect index of 20 may be realized by burning the methane gas and then releasing the combusted gas to the atmosphere, versus releasing the methane gas directly to the atmosphere. A greenhouse effect index of 20 is realized because burning methane yields a greenhouse effect index for CO2 of 1 and directly releasing methane gas to the atmosphere yields a greenhouse effect index of 21. Thus, taking the difference between these greenhouse effect indices, i.e. 21-1, yields a reduction of greenhouse effect index equal to 20. This reduction of greenhouse effect index can be traded as an emission credit.
For example, if developing countries such as China, CIS, etc. start business to effectively consume coal mine methane gas through receiving finance or loan aid from the Asian Development Bank, the World Bank, or ODA of Japan, etc., the enterprising body can make profits from the enterprise and also can make profits by selling CO2 emission credit to a surcharge payment obligator. This surcharge system is a system that a country (government) for example levies a toll on each enterprise for its releasing of carbon dioxide. There are two methods, one is that the surcharge is added to fuel price, the surcharge being proportional to the amount of carbon dioxide emission calculated from the amount of primary energy, and the other is that the surcharge is levied at the time carbon dioxide is actually released.